The subject matter disclosed herein relates to a method and device for measuring dimensions of features on or near an object using a video inspection device.
Video inspection devices, such as video endoscopes or borescopes, can be used to inspect a surface of an object to identify and analyze anomalies (e.g., pits or dents) on the object that may have resulted from, e.g., damage, wear, corrosion, or improper installation. In many instances, the surface of the object is inaccessible and cannot be viewed without the use of the video inspection device. For example, a video inspection device can be used to inspect the surface of a blade of a turbine engine on an aircraft or power generation unit to identify any anomalies that may have formed on the surface to determine if any repair or further maintenance is required. In order to make that assessment, it is often necessary to obtain highly accurate dimensional measurements of the surface and the anomaly to verify that the anomaly does not exceed or fall outside an operational limit or required specification for that object.
A video inspection device can be used to obtain and display a two-dimensional image of the surface of a viewed object showing the anomaly to determine the dimensions of an anomaly on the surface. This two-dimensional image of the surface can be used to generate three-dimensional data of the surface that provides the three-dimensional coordinates (e.g., (x, y, z)) of a plurality of points on the surface, including proximate to an anomaly. In some video inspection devices, the user can operate the video inspection device in a measurement mode to enter a measurement screen in which the user places cursors on the two-dimensional image to determine geometric dimensions of the anomaly.
In many instances, however, the object may be damaged in such a way that portions of the object may be missing (e.g., a turbine blade or other object may have a missing tip) or certain areas on the object are not sufficiently detailed in the image (e.g., along edges of a turbine blade where there are small dents caused by foreign object damage or the gap between the turbine blade and the shroud). A measurement of the missing portion or insufficiently detailed feature may not be possible since three-dimensional coordinates of surface points in the desired measurement area cannot be computed or are of low accuracy (e.g., if there are no surface points in the area of a missing portion, if the area is too dark, too bright, too shiny, or has too much glare or specular reflections, the area has insufficient detail, the area has too much noise, etc.). In other situations, the angle of view of the video inspection device may be such that the user cannot accurately place a cursor on at a desired location on the two-dimensional image to take a measurement. Furthermore, when viewing the image taken by the video inspection device, a user may not be able to appreciate the physical relationship between the probe and the object to adjust the view if necessary.